The invention is based on an rpm governor for fuel injection pumps as generally defined hereinafter. In a known rpm governor, or speed governor, of this kind (used in Bosch distributor injection pumps, Type VE), the idling spring is disposed between two levers and arranged parallel to a starting spring, which is likewise disposed between the levers and parallel to the idling spring. The idling spring, embodied as a helical compression spring, does not begin to come into play until the starting lever is pivoted, counter to the force of the starting spring, out of a position corresponding to an increased starting fuel quantity and into the idling position, in order to regulate, or govern, the idling speed during substantially load-free operation. To this end, a certain stroke length is available to the helical compression spring, before the two levers meet with frictional force--for instance when the load is increasing because of an adjustment or tensioning of the main governor spring, as well as when the load or driving resistance is decreasing and the rpm is accordingly increasing--causing the idling spring to be taken out of play for these operating ranges.
Especially when relatively low rpm is to be maintained during idling, the degree of nonuniformity (P-degree: degree of proportionality, or speed droop; the ratio between the increase in rpm from the rated rpm to the upper idling rpm and the upper full-load rpm) of the variation of the injection quantity over the rpm is high, so the differences between the characteristics or parameters affecting the idling rpm have a relatively great effect. Such parameters may be the combustion quality of the fuel and its readiness to ignite as well as frictional forces or tolerances in the pump itself. Frequently tolerances in the spring force of the idling spring, which do not manifest themselves until the pump is in operation, result in great differences in the residual fuel quantity supplied, for example for zero load, especially at the point when the idling spring ceases to be operative, which leads to considerable differences in the operation of a pump with mini-tolerances as opposed to maxi-tolerances. In this known governor, because of the space requirements, it is virtually impossible to adjust the idling spring, and hence the P-degree, retroactively, that is, in the installed state. The idling spring in these known governors is relatively stiff, so that despite the high P-degree a small degree of hysteresis can be attained, which primarily counteracts the jerking or bucking of the engine caused by the variable fuel preparation in the engine cylinders.
A further disadvantage is that in these known governors, there is a "hole" in the engine torque when switching over from overrunning to operation under load, with considerable impairment of the quality of driving, especially when the vehicle involved is a passenger car.